Development of 17-4PH stainless steel bimodal powder injection molding feedstock with the help of interparticle spacing/lubricating liquid concept

• PIM feedstocks are tailored to improve the shape retention.
• 25/75 wt.% finer/coarser powders gives the highest packing.
• Sintering distortions are connected to powder–binder separation during molding.
• Separation is eliminated for lubricating liquid fraction ≥ 0.08 and interparticle spacing < 0.5 μm.

Design of a powder injection molding (PIM) feedstock with proper selection of powder with unique particle size, particle shape and solid loading plays a significant role in controlling defects and distortion of PIM products. Using the concept of “interparticle spacing/volume fraction of lubricating liquid” 17-4PH stainless steel feedstocks with various bimodal powder combinations in thermoplastic polymer binder were designed and evaluated using both capillary and torque rheometers. Tendency to powder–binder separation, which is a factor indicating unacceptable distortions of sintered parts, is determined from the density variance during time-dependent viscosity measurement and thresholds in volume fraction of lubricating liquid as well as interparticle spacing parameters. The tailored feedstock with an optimum bimodal powder combination of coarse and fine particles exhibits suitable rheological performance with no evidence of separation and limited sintering distortion.

Figure optionsDownload as PowerPoint slide